Strawboard from vapor phase acetylation of wheat straw

Commercial ground wheat straw was used in a central composite response surface experimental design to examine four acetylating process variables: reaction temperature, reaction time, initial moisture content of straw, and the vapor flow rate of chemical reagent. The response variable was acetyl content determined as a function of straw weight gain. Diphenylmethyane diisocyante was used as a binder to prepare board samples with a hot press. Equilibrium moisture content (EMC) was determined at 65 and 90% RH at 27 degrees C, and dimensional stability was determined using a humidity cycle of 30-90% RH at 27 degrees C. ASTM D1037-93 standard method for a 3-point flex test was used to measure mechanical properties. The microstructures of both treated and untreated wheat straw and boards were observed with a scanning electron microscope. The vapor phase acetylation system used acetylated ground wheat straw to a 24% weight gain (dry weight basis). A mathematical model (R2 = 0.97) was developed to predict the weight gain as a function of the four acetylation processing variables. The maximum reduction in all strawboard properties occurred at the highest weight gain (24%). The strawboard EMC decreased (30% maximum reduction) as weight gain increased at both 65 and 90% RH. The strawboard dimensional stability increased as the weight gain increased (maximum reductions of 80% in thickness swell and 50% in linear expansion). The initial mechanical properties of the strawboards decreased as the weight gain increased (maximum reductions of 64% in strength and 48% in stiffness). The density of the strawboards decreased as the weight gain increased (23% maximum reduction). SEM micrographs showed no physical evidence of structural damage to cell walls from the acetylation.